In DE 197 35 759 has been described a method for control of an automatic driving device which has one propulsion source, one speed-change transmission with several toothed wheel sets that can be coupled, one fluid-actuatable main clutch and fluid-actuatable switch means for activating the individual toothed wheel sets. In addition, one electronic control is provided for the control of the main clutch and of the switch means, the main clutch being held in slipping state or attaining a change-over of the switch means free of traction interruptions. For shifting the forward gears one draw key is provided respectively on a transmission input shaft and on a transmission output shaft as coupling element or switch means respectively actuated by a hydraulic adjusting element for changing over the reduction steps or forward gears. At the same time, two loose toothed wheels respectively on the transmission input shaft and on the transmission output shaft can each be coupled with two fixed toothed wheels respectively on the transmission input shaft and the transmission output shaft.
The transmission input shaft has a central hole into which is movably passed one tappet which carries a draw key as form-locking coupling element. The draw key here protrudes a radial slot in the input shaft and interacts with longitudinal grooves in the toothed wheels. The length of the radial slot allows an axial displacement of the draw key via the tappet from a first position in which the draw key couples with positive fit a first toothed wheel with the transmission input shaft, to a medium idling position in which the draw key produces no connection with positive fit between the transmission input shaft and a toothed wheel and to a third position in which one other toothed wheel of a new ratio step is coupled with positive fit with the transmission input shaft.
To attain a low-wear complete shift of the draw key from one toothed wheel to the other toothed wheel, the cross-section of the opening of a throttle valve of the internal combustion engine is reduced for a brief time in the shifting torque independently of an accelerator pedal input in order to reduce the input torque of the internal combustion engine to the range of from milliseconds to tenths of seconds.
However, this known method for control of an automatic driving device has the disadvantage that during a higher traction shift under load, the draw key or the shifting element has to be disengaged from the toothed wheel for which strong shifting forces are needed. To reduce said shifting forces, it has been proposed to reduce to the switch torque the drive torque of the internal combustion engine. But due to said procedure, the drive train of a motor vehicle is completely discharged for a long period of time, which results in an undesirable traction interruption.
Therefore, the problem on which this invention is based is to make a method available for control and regulation of a drive train by means of which a high traction shift can be carried out quickly and without interruption of traction with great shifting comfort.